Electrically conducting coating on



J. M. MOCHEL Sept. 30, 1952 ELECTRICALLY CONDUCTING COATING ON GLASS AND U'I'HER CERAMIC BODIES Original Filed Sept. 5. 1947 Jnhmlut Jn/v M Mac/ffl.

Stimme? Ressued Sept. 30, 1952 ELECTRICALLY CONDUCTING COATING N GLASS AND OTHER CERAMIC BODIES John M.`Mochel, Louisville. Ky.. assignor to Corning Glan Works. Corning ration of New York N. Y., a corpo- Orlginal No. 2,564,987. dated August 2l, 1951. Se-

rial No. 771.860, September 3, 1947.

Application for reissue May l5, 1952, Serial No. 288.009

1 Claim.

Matter enclosed in heavy brackets I: :l appears in the original paient but forms no part of this rebelle speclilcationgmatter printed in italics indicates the additions made by reissue.

This invention relates to glass articles and other ceramic bodies having electrically conducting oxide coatings of the kind known generally as iridized coatings. When glass or other vitreous ceramic body is heated and contacted with certain metal salts, either in the form of fumes or atomized solutions thereof. a strongly adherent layer of an oxide of the metal is formed on its surface. This process is known as iridizing because the coatings thus produced are frequently iridescent due to interference of iight waves reilected from the extremely thin oxide lms.

The application of iridizing to glass for the production of beautiful art ware is quite old and for this purpose salts of tin and of iron are employed. More recently it has been found that tin iridiaed coatings have a suillciently low electrical resistivity at normal temperature to permit their use on high-tension electric insulators for the purpose of [decreasing] spreading the lpotential gradient on the surfaces of the insulators and thus preventing corona and radio interference. United States Patent 2,118,795, issued May 2, 193B, to Jesse T. Littleton, discloses the use of tin iridized coatings on electric insulators for such a purpose. For some purposes the tin iridized coatings are not suitable.

One o1 the chief objects of this invention is to produce on glass and other non-porous ceramic surfaces electrically conducting coatings which are permanently incorporated with the glass or ceramic surface, and which have suiliciently low electrical resistivities to permit the use oi such articles for electric heating devices.

Another object is to provide transparent electric resistance elements for use in electric heating devices such as ovens, broiiers. toasters, flat irons. grills, space heaters, and the like.

Another object is to provide glass bodies having lridized coatings of predetermined electrical resistance.

Another object is to provide a conducting iridized coating which consists of an oxide of in dium.

Another object is to provide a conducting iridized tllm which consists of an oxide of indium.

In another application Serial Number [771,- 861,] 771.859, filed September 3, 1947, now [abandonedI illed by me concurrently herewith] Potent No. 2,564,707, issued August 21, 1951, I have described [and claimed] iridized lllms comprising an oxide of indium and an oxide of tin. An electric resistance device embodyina auch a film. as an element is claimed in my application Serial Number 197.515, illed November 24. 1950. now Patent No. 2.564.709, issued August 21, 1951.

2 The present invention is directed to similar films composed oi an oxide of indium alone, and to ceramic surfaces coated therewith to be hereinafter more fully described and illustrated in the accompanying drawing in which:

Fig. l is an elevation of an apparatus for iridizing glass sheets in accordance with the invention;

Fig. 2 is a vertical sectional view of an electrically heated device for toasting bread made in accordance with the invention.

I have discovered that films composed of indium oxide and produced by iridization with a salt of indium, have relatively low electrical resistivities and can be used for various purposes.

The electrical properties of the new oxide nlms are influenced by various factors including thickness of the films, the temperature at which the films are produced and the relative expansion coedicients of the films and the glass or ceramic body upon which they are deposited, as will hereinafter be more fully explained.

The thickness of the iridized 111m may be gauged -by the apparent color of the tllm caused by interference of light reflected therefrom. As the thickness of the film increases, its apparent color changes and the order of succession of the colors with increasing thickness is analogous to that of the well-known Newton rings described in A Treatise on Light." by R. A. Houstoun. Longmans, Green 8: Co., Ltd. (i938). page 147, as follows:

ist order-white, yellow, red,

2nd order-violet, blue. green. yellow, red. 3rd order-purple, blue. green, yellow. red, 4th order-green. red.

5th order-greenish-blue, red,

6th order-greenish-blue, pale red,

7th order-greenish-blue, reddish-white.

Obviously. a nlm of uniform thickness will appear to be of one color only. A slight non-uniformity in film thickness at the edge of the plate will produce suillclent color sequence to identify the order of thickness of the main portion of the film. As a further aid, a long strip of glass may be lridized by directing the spray at one end thereof whereby the various orders of colors will be spread longitudinally oi' the strip and will serve as a convenient comparison. Since reci marks the ends of each order, this color is preferably employed as the distinguishing mark of the successive orders. For present purposes. red light has a wave length of 6200 Angstroms. Calculation shows that the approximate nlm casse Angstroms` answera- PFP.

The common unit of electrical resistivity of any material is the ohm cm." which ls the resistance in ohms between two opposite faces of a cube oi' the material, each dimension of which is 1 cm. For a square film of material the electrical resistivity therefore becomes the resistance in ohms multiplied by the thickness of the illm in centimeters. For convenience the resistance in ohms of a square film of third order red is herein employed as the unit of speciiic resistance and in order to avoid confusion it is designated standard resistance. The resistivity may be calculated by multiplying the standard resistance by the thickness in centimeters of a third order red film (3870x -l cm.).

The iridized films of this invention may be formed advantageously upon the surface of a glass article, such as a glass sheet. They are preferably produced by heating the glass uniformly to an elevated temperature which may be about 500 C. or above. and atomizing a solution containing indium chloride as a ilne mist upon the heated glass for a length of time'sumcient to produce an iridized nlm of the desired thickness and electrical resistance.

The atomized solution is preferably directed perpendicularly against the surface to be coated for a time. usually 10 to 20 seconds. which will depend upon the rate of atomization, concentration of the solution. the desired thickness of the film, etc. To some extent the thickness will govern the electrical resistance of the film. the resistance becoming generally lower as the thickness is increased. The electrical resistance may be measured with an ohmmeter during iridizing. For this purpose and for subsequent use in the application of electric current to the iilm. permanent electrical contacts therewith may be provided on the glass plate before iridlzing takes place. This may be accomplished by metalllzing two opposite edges of the glass plate, as by the application thereto of a platinizing solution which is red on ln the usual manner to provide adherent bands or stripes of metallic platinum on the glass.

In the drawing. Fig. l illustrates one form of apparatus' for carrying out the above-described process. A glass plate I0, provided with platinized stripes I I (shown on an exaggerated scale) on two opposite edges. is about three inches square between the stripes Il. It is heated uniformly on an electric hot plate I2. An atomizer, generally designated il and preferably composed of glass, comprises a cup Il for containing the solution to be atomized. an atomizing nozzle il and a tube It for the introduction of compressed air to the nozzle. The atcmlzer is supported above the glass plate ill so that the nozzle It is about one foot above the glass plate. An ohmmeter i1 is provided with two contact leads I8 which may be brought into electrical contact with stripes il (ss shown) before atomization. As atomization proceeds and a conducting iridised iilm is formed on the glass. the electrical re- 4 sistance which is registered by the ohmmeter decreases from an initial inilnite value as the thickness of the nlm increases. When the electrical resistance attains the desired value. atomization is stopped by cutting oil' the supply of compressed air from the atomiser Il.

The following example will illustrate but does not limit the invention: 5.3 g. of pure indium chloride (InCla) were dissolved in 8 cc. of water and 2 cc. of concentrated aqueous hydrochloric acid and the solution was atomiaed for ten seconds on a plate of heat-resisting borosilicate glass which was heated at '100 C. The resulting film of indium oxide was transparent and had a standard resistance" of 875 ohms [per aquarel. When the iridized plate was heated at 250 C. for 2 hours. the "standard resistance at room temperature was lowered to 465 ohms [per aquarel. The resistance of the nlm may also be lowered by increasing the time of iridization which increases the thickness of the nlm.

In lieu of indium chloride, other salts of indium may be used whereby results similar to those set forth above may be obtained.

To illustrate electric heating devices made in accordance with this invention, reference is had to Fig. 2 in which two glass plates 20 are provided on opposite edges with platinized stripes il and 22 (shown on an exaggerated scale) and iridized films 23 (also greatly exaggerated). The plates Il are supported in spaced parallel relation on a dielectric base 24 by metal strips 2B which are attached to the platinized stripes Il. The metal strips 2l are secured to the base 24 by binding posts 2i to which a wire 21 forming one side of 'an electric circuit is connected. The other side of 'the circuit is electrically connected with the platinized stripes 2|. From this it will be seen that the iridized lms 2l are electrically connected in parallel. Between the glass plates 20 is located a slice of bread I8 to be toasted and the entire assembly is surrounded by a protecting shell 2l.

Other arrangements of the various parts of the device shown in Fig. 2 and modifications thereof for other purposes will be apparent to those skilled in the art and are included within the scope of the invention as claimed.

I claim:

An electric resistance device comprising a nonporous. vitreous, ceramic body having on a surface thereof an electrically conducting. iridized metal-oxide film integrally united with the surface and consisting essentially of indium oxide, said body being provided with spaced terminals in electrical contact with such tllm.

JOHN M. MOCHIEL.

REFERENCES CITED The following references are of record in the ille of this patent or the original patent:

UNITED STATES PATENTS Number Name Date 2,026,006 Farncomb Dec. 3l. 1935 2,118,795 Littleton May 24, 1938 2,194,189 Wheeler et al Mar. 19, 1940 2,429,420 McMaster Oct. 21. 1947 2,518,663 Zunich July 25. 1950 OTHER REFERENCES Versatile indium, Rose. Scientific American, April 1944. Dil. 154-156. 'i5-In. D.

Thiel et al.: Chem. Abstracts (Sept-Dec. 1910) vol. 4, pp. 2613-2616.

Disclaimer Re. 23.5.55.-J0/m M. Moebel, Louisville, Ky. ELECTRICALLY CONDUCTINU (fm'rmu 0N GLASS AND OTHER CERAMIC BODIES. Patent dated Sept. 30, 1952. Disclaimer filed Feb. 16, 1954, by the assignee, jorfnzfnf/ (Nm3 Works.

Hereby enters this disclaimer to the single claim of said reissued Letten` PatentA [Official Gazefte March 16', 1954.] 

